*2.2. Establishment of the SD Model*

The structure optimization model of PLE space is realized by constructing the system dynamic model. First, it is necessary to clarify the system boundary and system structure. The system boundary affects the model's complexity, and the boundary cannot be too large or too small. The system structure refers to the variables involved in the model and the relationship between them. The purpose of this research is to understand the interaction between the main elements in PLE space. Therefore, the system boundary was confined to Zhaotong from 2010 to 2017, and the model was constructed by selecting factors related to population, social fixed asset investment, regional GDP, land resources, and more. The PLE space system is divided into a population–economy subsystem and a land-use subsystem. According to data recorded by the Statistical Yearbook of Zhaotong and Statistical Bulletin of Zhaotong, 33 variables were finally selected. The system structure is shown in Figure 4. Specific variable names and units are detailed in Table S1 of the supplementary file.

The relationship between system variables and mathematical equations is the core of the model construction, and it influences the accuracy of the model. In this paper, the comprehensive empirical method, regression analysis method, logical inference method, weighted average method, and other methods are used to determine the equation parameters. Moreover, the Lookup function and conditional function provided by Vensim software were fully utilized, and 33 groups of equations were finally determined (see Equations (S1)–(S33) in the methods and data of the supplementary file for details).

The simulated values were compared with the actual values of some variables from 2010 to 2017, and the results are shown in Table S2. The absolute values of the errors are in the range of 0–5%, which indicates that the constructed model can respond to the interrelationships among the elements within a reasonable range and can be used for future simulation.
